B25SS Rocker Box Studs

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B25SS Rocker Box Studs

Post by Cocker Cox » Thu Jul 09, 2020 3:07 pm

Hi, All,

I’m currently refurbishing the top-end of my B25SS and have removed the rocker box studs to check their lengths as a couple seemed a bit short. The length of one pair of studs (part numbers 21-2092) is not given in the manual but Googling the part number gives a 3-1/4” stud. However, another pair of studs (part number 14-1628) is given in the manual as also being 3-1/4”, but being of special steel (EN16R). I wonder why this pair of studs is (was) made of special steel and would modern replacements be so? My other problem is, one of the pairs removed (either 21-2092 or 14-1628) are short at 3”, but I can’t remember which they were!
Last edited by Cocker Cox on Thu Jul 09, 2020 7:25 pm, edited 1 time in total.

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Re: B25SS Rocker Box Studs

Post by minetymenace » Thu Jul 09, 2020 4:12 pm

I'm guessing the "special" ones are the ones which support the engine steady. I think the last time I did this, it cost me a couple of pints and a mate turned up some studs for me, I lent him the rocker box and he gave me plenty of thread on the ends which I cut to length.....helicoil kit at the ready for the head!

When/if you get some made, please publish the lengths in this post for future reference....ta!
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Re: B25SS Rocker Box Studs

Post by Cocker Cox » Thu Jul 09, 2020 7:22 pm

Thanks for that. Yes, looking at the parts catalogue, they are the ones for the head steady. Curiously, the other pair of studs I removed are actually 3” not 3-1/4”, and I have no reason to believe they’re not original; this makes sense... why would they be the same length as the ones holding the head-steady bracket? Both studs are available from Draganfly by the way... and their web-site reports high stocks of both!

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Re: B25SS Rocker Box Studs

Post by crankbuster » Thu Jul 09, 2020 7:25 pm

Not that it matters too much these days, but it was actually the studs in the dowel positions that were stronger steel.
Here is my rockerbox video, Starfire not SS though
https://youtu.be/kws1ISPPMBY

I think the stud lengths are given OK in the Parts list, but not the workshop manual.
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Re: B25SS Rocker Box Studs

Post by Cocker Cox » Fri Jul 10, 2020 7:27 am

Yes, it’s interesting... two pairs of the studs are special steel, including the locating dowel studs, but not the head-steady ones. I can see why the head-steady studs might be, but not the locating dowel studs or the other, rear pair. There must have been a reason. I’m still unsure about the 14-1628 studs being either special steel or 3-1/4” though (the same length as the head steady ones). Mine are 3”, which makes sense to me. As we know, the parts catalogues are full of inconsistencies so maybe this is one of them (the length of the head steady studs isn’t given and is not marked as being special steel).

On the subject of studs, a couple of mine were corroded into the head and rocker box. Should I use copper-slip, both on the threads and on the shanks?

One final question(?!), the exhaust valve spring top cap catches on the wall of the rocker box, making separating it from the cylinder head difficult. On my Starfire, the valve spring top cap actually chaffed on the rocker box wall in operation. I noticed that the inlet side of the rocker box had been machined by the factory to give clearance, so this was clearly an issue. Should I remove some material to address the issue or leave it as-is?

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Re: B25SS Rocker Box Studs

Post by minetymenace » Fri Jul 10, 2020 8:15 am

I would try to identify if it is the rockerbox out of shape or the head and then make a decision. It could be a number of things, valve guides out, bad casting etc and the solution depends on the cause to some extent. If there is a possibility of something moving touching something stationary, it needs sorting, and this may well involve removing material to produce clearance or moving valve guide or whatever.

If it is just catching and hindering the unit being dismantled, it is your choice, but IMHO these engines go together well and are not generally subject to this sort of thing, so there is probably an obvious cause.
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Re: B25SS Rocker Box Studs

Post by crankbuster » Fri Jul 10, 2020 2:39 pm

With acknowledgement to Steve at SRS Publishing:
They were a number of changes to the head studs:
Headstuds.jpg

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Re: B25SS Rocker Box Studs

Post by Ian Hingley » Fri Jul 10, 2020 8:59 pm

crankbuster wrote:
Fri Jul 10, 2020 2:39 pm
With acknowledgement to Steve at SRS Publishing:
They were a number of changes to the head studs:
Headstuds.jpg
Hand drawn revision notes. Takes me back to the drawing offices of the late 70s / early 80s. Shudder!

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Re: B25SS Rocker Box Studs

Post by gunnag » Sat Jul 11, 2020 12:33 am

If it was my bike I would remove the studs, run a flat file over the rocker cover surface, then helicoil all the stud holes with a suitable thread form (I used m6 on my B44) and replace with socket caps. The two bolts holding the head steady are probably strong enough and can be left alone. But its worth counterboring the holes in the rocker cover so that the socket caps sit just proud, use a fibre washer under the socket cap heads to stop leaks. You will have to get socket caps of the right length. This method allows easy removal of the rocker cover and head.

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Re: B25SS Rocker Box Studs

Post by minetymenace » Sat Jul 11, 2020 12:11 pm

Good advice gunnag, but I'm worried you have been influenced by beat ref the metric threads.....you will be advocating synthetic oil and electronic ignition soon!
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Re: B25SS Rocker Box Studs

Post by Momus » Sun Jul 12, 2020 3:03 pm

gunnag wrote:
Sat Jul 11, 2020 12:33 am
If it was my bike I would remove the studs, run a flat file over the rocker cover surface, then helicoil all the stud holes with a suitable thread form (I used m6 on my B44) and replace with socket caps. The two bolts holding the head steady are probably strong enough and can be left alone. But its worth counterboring the holes in the rocker cover so that the socket caps sit just proud, use a fibre washer under the socket cap heads to stop leaks. You will have to get socket caps of the right length. This method allows easy removal of the rocker cover and head.
I wouldn't want to be too picky but fiber washers under a cyclically loaded valve rocker carrier is not a good idea.

Provided the head seating surface was reasonable, the SHCS straight onto the aluminium should be fine. If you were worried a thick - 060" copper washer wouldn't hurt.
If you love it, lube it.

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